Corrosion resistant beryllium bodies

ABSTRACT

1. A BERYLLIUM BODY HAVING AN ELECTROLTICALLY DEPOSITED CRYSTALLINE BERYLLIUM OXIDE COATING ADHERENT TO THE BODY SURFACE PRODUCED BY IMMERSING THE UNCOATED BODY IN A BATH CONSISTING ESSENTIALLY OF WATER, SODIUM CHROMATE IN AN AMOUNT AT LEAST 0.4%, BY WEIGHT, OF THE BATH, AND AN AMOUNT OF CHROMIC ACID SUFFICIENT TO ADJUST THE PH OF THE BATH INTO A RANGE FROM ABOUT 5.5 TO ABOUT 7.5, THE TEMPERATURE OF THE SAID BATH BEING BELOW ABOUT 130* F., AND PASSING AN ELECTRIC CURRENT TO THE SURFACE WITH THE SURFACE CONNECTED AS AN ANODE.

United Sores Patent @ce 3,694,331 Patented Sept. 26, 1972 3 694 331 CORROSION RESISTAN'l BERYLLIUM BODIES Louis J. Csontos, Parma, and Albert James Stonehouse,

Lyndhurst, Ohio, assignors to Brush Beryllium Com- A further object is to provide beryllium bodies resistant to corrosion in high temperature air, water, deionized water, and salt spray environments.

A still further object of the invention is to provide a pany, Cleveland, Ohio method for applying a corrosion resistant coating to the No Drawing. Continuation of application Ser. No. beryllium Surface f b di 9, 11, 1967 which Is a dlvlslo" of lf- Another object of the invention is to provide a method ii l 5 6 g a 33 for anodizing the beryllium surfaces of bodies to render app canon f fi b b' them corrosion resistant to high temperature, water, de-

US. CL R 1 Claim 10 ionized water, and salt spray environments.

Other objects and advantages of the invention will be- This plication is a con i a n of pp come apparent from the following description.

No. 670,486, filed Aug. 11, 1967, whic i a s on of The method comprises applying a protective surface our pending application Ser. No. 395,012, filed Sept. 8, coating to beryllium surfaces of bodies by passing an elec- 1964 and titled Corrosion Resistant Beryllium Bodies tric current to the beryllium surface connected as an anode, and Method for Producing Same, and which is directed in a bath consisting essentially of water, sodium cromate to the method and bath, the present application being in an amount of at least 0.4%, by weight, of the bath, and directed to the berryllium body. an amount of chormic acid sufiicient to adjust the pH This invention relates generally to beryllium bodies havrange of the bath from about to about Preferably ing a corrosion resistant surface coating, and to a method to about for application of suchacoating The concentration of the sodium chromate solution More specifically, the invention relates to anodized igi g g to beryllium bodies having a corrosion resistant surface coat- 0 e a an pre y 15 use a 1 0 Welg d t m thud f r anodizin th surface of said concentration. The use of sodium chromate in excess of L an o a e o g e 10% does not appear to increase the effectiveness of the 0 method or coating appreciably.

g l f mfital h become well estabhshed for aPPh' The bath should be free of hydrochloric and sulfuric cations in inertial guldance systems, structural components acids as their presence prevents f ti f the desired for aircraft and aerospace use, and in other fields where protective coating its Properties of lightness, high Strength at elevated o The temperature of the bath must be maintained below Pofaturos and hlgh Strength to Wolght l'atlo dosll about 130 F., since the coating applied above this temablo oharaotorlstlosperature does not afford proper protective resistance. The

However, commercially available beryllium 1s sub ect temperature of the bath should be less than 130 -F., rangto corrosion by various environments, including high teming from about 70 F. to about 110 F., and is preferably perature air, tap water, deionized water, and salt spray. about 75 F, Various attempts have been made to p de corrosion For optimum resistance of the protective coating, the resistant beryllium materials. Ceramic coatings have been solution of sodium chromate, should be prepared with pp to beryllium Surfaces, r o s met ods of distilled water and the pH adjusted with reagent grade anodizing beryllium surfaces have been used, but all such 40 h i id, Th current density may v f b ut previously developed methods have failed to provide the 48 to about 300 amperes per square foot, and is preferdesirable combination of properties obtained by the preS- ably maintained at from about 150 to about 200 amperes ent method. per square foot.

The present method provides corrosion resistant beryl- Examples of beryllium bodies protectively coated by lium materials which greatly extend the application of the method of the invention and exposed to high-temperabofyllium in Various fields, and was developed as a result ture air environment are presented in the following Table of extensive investigation. I. In each example, a beryllium coup-on 0.50" wide, 1.25"

A primary object of the invention is to provide anodized long and 0.1875" thick was protectively coated under the corrosion resistant beryllium bodies. 50 various processing conditions set forth in Table I.

TABLE L-PRooEss VARIABLES Wt. cone. Tempera- Current of sodium ture of Hours tested Physlcalcondltlon density, Time chromate, bath in in 800 C. of specimen after Example No. Voltage amps/ft. (min. percent pH F. dry air test exposure Efieet or anodizing time 12 170 10 5 7. 0 75 96 No attack or failure. 12 177 20 5 7.0 75 96 Do. 12 166 30 5 7.0 75 96 D0. 12 17a 40 5 7.0 75 96 Do. 12 162 50 5 7.0 75 96 Do. 12 166 5 7.0 96 Do.

Effect of current density 10 49 e0 5 7.0 75 96 No attack or failure.

9 99 60 5 7.0 75 96 D0. 12 60 5 7.0 75 96 Do. 12 199 60 5 7.0 75 96 Do. 12 29s 60 5 7.0 75 96 Do.

Effect of solution concentration 12 166 so 1 7. 0 75 161 No attack or failure. 12 so 2 7.0 75 161 Do. 12 162 60 5 7. 0 75 161 Do. s 160 60 10 7.0 161 Do.

TABLE I-Contlnued Wt. conc. Tempera- Current of sodium ture of Hours tested Physical condition density, Time chromate, bath in in 800 C. of specimen after Example No. Voltage amps/ft. (min) percent pH F dry air test exposure Effect of increased voltage 18 162 10 1. 7. 0 75 282 No attack or failure. 24 96 0. 6 7. 0 75 282 D0. 24 166 10 1 7. 0 75 137 Do. 60 160 30 0.4 7.0 75 96 D0.

Effect of temperature variation Hours tested in 1,489 F.-

dry air 12 160 5 7 0 111 203 No attack or failure. 12 160 60 5 7 0 176 65 Failed, corroded. 12 160 60 5 7 0 140 65 D0. 12 160 60 5 7 0 75 203 N0 attack or failure. 12 160 60 5 7 0 129 174 Do.

Table II shows the effect of exposure to various testing face of the base metal, the overall dimensional change environments of bodies protectively coated at the process is less than 0.0001" per side, during application time of conditions specified in the table. up to 60 minutes. The small dimensional change in the TABLE II -EXPOSURE TESTS OF ANODIZED BERYLLIUM BODIES Duration of test, Example No. Beryllium body size Test environment hrs. Condition of bodies 1 1" high x i6" diameter. 800 C. in 1% moist air 1, 749 No attack or failure or auodic coating. 850 C. in dry, C01 free air..- 185 D0. 900 C. in dry CO1 free air. 137 Do. 1,000 C in dry 002 free air.. 137 Do.

700 C. in dry or 100 N 0 attack of failure of anodic coating, wt. gain 20.1 m ./cm.

7 z x x 36 817 C. in dry 0: 60 No attack or failure of anodlc coating, wt. gain= 0.33 nigh/cm). 8 $5 1: x 14" 1,030 C. in dry or N0 attack or failure of anodlc coating, wt. gain= 0.58 mg./cm. 9 3 thick is 2M0" diameter 5% NaCl salt spray... 120 No attack or failure of anodic coating. 3" x 1" x 36". 20% NaCl salt spray- 24 Do. 110 F. deionized water- 1,656 Do. Tap water 2, 160 Do. 0.1 N NaCl solan 336 Do:

All specimens included in Table II were anodized in a bath containing 5 weight percent sodium chromate with the pH adjusted to 7.0 with chromic acid at a temperature of 75 F., 12 volts and a current density of 160 amperes/ft.

It will be noted from Tables I and II that all the bodies surface is the result of replacement of the removed berylwith the exception of those protectively coated in lium by a protective coating, the volume of which is Examples 21 and 22 of Table I at a bath temperature approximately equivalent to that of the removed metal. above 130 F., were completely protected from oxidation. Thus, the negligible dimensional change which occurs No failure of the protective coating other than a slight 50 in the surface during application of the protective coating change in color occurred, during test exposure of body is unexpected, as beryllium oxide is known to occupy a specimens of all the other examples. Commercial beryllarger volume than the amount of beryllium metal stoilium when exposed to the same conditions normally chiometrically required to produce a given quantity of oxidizes after 48 hours exposure to the extent that to oxide. The final surface of the protectively coated body is 50% of the test pieces will have been reduced to a fluffy identical in surface pattern with the original body surface,

powdered oxidation product. as the degree of polish, machining marks, and blemishes A comparison exposure test of commercial beryllium are faithfully reproduced.

specimens with the anodized bodies of Examples 6-8 in- The coatings a li d b th th d of th i ti elusive, of Table Showed that after posu e in 0118 are quite dense and relatively thick. Generally, the thickatmosphere of y oXygen at for 75 hours, ness of the coating varies from 0.1-2.4 mils, but preferf 45 hours, 5 1030 f 35 flours, the ably is about 0.5 mils, dependent upon the control of the mercial specimenszmcurreda weight gain of 17.0, 63.0, process conditions a 53 3: 2 32 g ifig g i g g ggg sgg fifiz The protective coating applied is believed to be a form n f thou h th cfmnfercial Syecimens were of hydrated beryllium oxide as it IS nearly amorphous 1n examp es eve g e t 1 t the initially deposited form, as indicated by X-ray analysis. tested for a shorter time at aliproxlma e y same When heated at elevated temperature for a sufficient time, peratures. The examples thus illustrate the high corrosion resistance of the beryllium bodies, the surfaces of which i coating converted to norma} crysialhne f are coated in accordance with the method of the invenhum oxide as evidenced by X'ray dlfiractlon analysls' 7 Temperatures of about 800 C. may be employed for tion.

The examples are presented as illustrative embodiments efiecmlg converslon f the crytanmfi State- Having thus described our invention, we claim:

of the invention and include the preferred embodiments I known at the time of preparation of the specification. A befylllum y having an electrolytically deposlted Although the method of applying the protective coating crystalline beryllium oxide coating adherent to the body to beryllium bodies results in some dissolution of the sursurface produced by immersing the uncoated body in a perature of the said bath being below about 130 F., and 5 passing an electric current to the surface with the surface connected as an anode.

References Cited UNITED STATES PATENTS 2,437,620 3/1948 Speer 204-58 6 OTHER REFERENCES Levin, M. L.: The Formation of Crystalline Anodic Films on B6, Transactions of The Faraday Soc., vol. 54, pp. 935-940, 1958.

Whitby, L., et al.: Chromic Acid Anodizing of B, Proceedings of the A.E.S., vol. 48, pp. 106-108, 1961.

Missel, Leo.: Chromic Acid Anodizing of B, Proc. of The A.E.S., vol. 48, pp- 109-111, 1964.

10 JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner 

1. A BERYLLIUM BODY HAVING AN ELECTROLTICALLY DEPOSITED CRYSTALLINE BERYLLIUM OXIDE COATING ADHERENT TO THE BODY SURFACE PRODUCED BY IMMERSING THE UNCOATED BODY IN A BATH CONSISTING ESSENTIALLY OF WATER, SODIUM CHROMATE IN AN AMOUNT AT LEAST 0.4%, BY WEIGHT, OF THE BATH, AND AN AMOUNT OF CHROMIC ACID SUFFICIENT TO ADJUST THE PH OF THE BATH INTO A RANGE FROM ABOUT 5.5 TO ABOUT 7.5, THE TEMPERATURE OF THE SAID BATH BEING BELOW ABOUT 130* F., AND PASSING AN ELECTRIC CURRENT TO THE SURFACE WITH THE SURFACE CONNECTED AS AN ANODE. 